Device at medullary nails for fixation of bone fragments at bone fractures

ABSTRACT

The present invention relates to a device at medullary nails for fixation of bone fragments at bone fractures, wherein a medullary nail ( 5 ) is insertable into holes ( 6 ) in medullary canals in the bone fragments. Front parts ( 5   b ) of the medullary nail ( 5 ) can be locked to one of the bone fragments by means of a locking means ( 9 ) which is transversely located in the bone fragment and extends through a transverse hole ( 10 ) in said front parts ( 5   b ) of the medullary nail ( 5 ). The front members ( 5   b ) of the medullary nail ( 5 ) includes a snap-in device ( 11 ) for attaching with a snap-in action the medullary nail ( 5 ) to the locking means ( 9 ).

The present invention relates to a device at medullary nails forfixation of bone fragments at bone fractures, wherein a medullary nailis insertable into holes in medullary canals in the bone fragments,wherein front parts of the medullary nail can be locked to one of thebone fragments by means of a locking means which is transversely locatedin the bone fragment and extends through a transverse hole in said frontparts of the medullary nail.

In order to fix the front members of a medullary nail at a bonefragment, one can use a locking means e.g. in the form of a screw whichis screwed into a predrilled, transverse hole in the bone fragment andthrough a transverse hole in said front parts of the medullary nail.

When screwing the screw into the bone fragment, said screw often ends upobliquely relative to the transverse hole in the medullary nail, and forbeing able also in such cases to screw said screw through said hole,said hole must have a substantially larger or at least a great deallarger diameter than the screw. This means however, that there will be aplay between the medullary nail and the screw so that the medullary nailcan move particularly in torsional directions but also in axialdirections relative to the screw. This in turn, means that the bonefragments will be able to move relative to each other, i.e. the fixationwill not be stable.

It is also very difficult to hit the hole in the medullary nail with adrill by means of which the transverse hole is drilled. This is doneduring radioscopy and it is very common that the surgeon is forced todrill several times on different locations, which results in a stronglyweakened bone, while simultaneously the surgeon and the patient aresubjected to radiation for an unsuitable long time.

On ulna, radius and fibula, it is not possible to use conventionalmedullary nails and securing said nails with transverse screws, becausethe medullary canal in these bones is too small for being able to usemedullary nails having sufficiently large diameter for providing themwith the required large hole for a transverse screw.

The object of the present invention is to remedy, these problems andaccomplish that the medullary nail can be fixed substantially immovableat the locking means. This is arrived at by providing the deviceaccording to the invention with the characterizing features ofsubsequent claim 1.

Since the medullary nail has a snap-in device, allowing said nail to besnapped-in onto the locking means, it is accomplished that the frontmembers or parts of the medullary nail can be fixed substantiallyimmovably at the locking means. Furthermore, the snap-in device can bedesigned such that the locking means easily captures the medullary nailwhen said nail is threaded into the medullary canal.

The invention will be further described below with reference to theaccompanying drawing, in which

FIG. 1 is a longitudinal vertical section of a forearm bone with amedullary nail according to the invention; and

FIGS. 2, 3 and 4 illustrate a longitudinal horizontal section of frontparts of the medullary nail of FIG. 1 in different positions relative toa locking means during a fixation movement at which the medullary nailis fixed at the locking means.

The forearm bone 1 (ulna) illustrated with a section in FIG. 1 has abone fracture 2 at which the forearm bone 1 is broken in two or morebone fragments, e.g. an upper bone fragment 3 and a lower bone fragment4.

These bone fragments 3, 4 are fixed relative to each other by means of amedullary nail 5 which is inserted in a hole 6 which has been drilled inthe longitudinal direction in the medullary canals of the bone fragments3, 4. In the upper bone fragment 3, a number of holes, e.g. twotransverse holes, have been drilled for two transverse locking screws 7,8 or corresponding locking means which extend through two transverseholes in rear parts 5 a of the medullary nail 5. The transverse lockingscrews 7, 8 are adapted to fix the upper bone fragment 3 and the rearparts 5 a of the medullary nail 5 relative to each other. In the lowerbone fragment 4 a transverse hole has been drilled into which atransverse locking screw 9 is screwed. This locking screw 9 is adaptedto extend through a transverse hole 10 in front parts 5 b of themedullary nail 5. The locking screw 9 is adapted to fix the lower bonefragment 4 and the front parts 5 b of the medullary nail 5 relative toeach other and it can be extracted from the hole 10 by being backed outtherefrom and from the hole therefor in the lower bone fragment 4.

The instrument for drilling a longitudinal hole in the medullary canalfor medullary nails 5 and transverse holes for locking screws, arecommonly known and therefor not further described.

The front parts 5 b of the medullary nail 5 has a snap-in device 11 forattaching by snap-in action said front parts 5 b to the transverselocking screw 9. The snap-in device 11 is designed to be threaded ontothe locking screw 9 by moving it in a forward direction in the hole 6 inthe medullary canal as is shown with an arrow F in FIGS. 2 and 3.Hereby, the snap-in device 11 is brought to be opened by the lockingscrew 9—as is apparent from FIG. 3—and when the locking screw 9 issituated in the hole 10, the snap-in device 11 will snap-in to itsclosed condition—as is shown in FIG. 4—which means that the snap-indevice 11 retains the medullary nail 5 at the locking screw 9.

The snap-in-device 11 is preferably designed such that it can hold themedullary nail 5 at the locking screw 9 with a firm grip such that themedullary nail 5 can move neither in axial direction relative to itslongitudinal axis L nor rotate relative thereto.

The snap-in device 11 is also preferably designed such that it can notloosen or be drawn away from the locking screw 9.

The snap-in device 11 can be designed in different ways for obtainingthe abovementioned snap-in result at the locking screw 9. The snap-indevice 11 illustrated in the drawings has two jaws 12, 13 which definebetween them a gap 14 which is open in forward direction and of whichinner parts 14 a are open towards the hole 10. Said inner parts 14 a ofthe gap 14 has a smaller width than the hole 10 and the diameter of thelocking screw 9. The jaws 12, 13 are elastic such that the locking screw9 brings them to spring in a direction from each other when the snap-indevice 11 is threaded thereon. When the snap-in device 11 has beenthreaded so far onto the locking screw 9 that said screw is situated inthe hole 10, the jaws 12, 13 have sprung back to their startingpositions due to their elasticity, whereby said jaws 12, 13 retain themedullary nail 5 on the locking screw 9.

The jaws 12, 13 can be provided such that the gap 14 tapers successivelyin a direction towards the inner parts 14 a thereof and to the hole 10.The jaws may further be provided such that outer parts 14 b of the gap14 are rather much wider than the diameter of the locking screw 9, whichmeans that the snap-in device 11 is easier oriented (if necessary byrotating the medullary nail 5 somewhat about its longitudinal axis L)relative to the locking screw 9 when said device shall be threaded ontosaid screw.

In the embodiment shown, the snap-in device 11 has a keyhole like shapedefined by the gap 14 between the jaws 12, 13 and the hole 10. Seen inthe longitudinal direction of the medullary nail 5, the jaws 12, 13 havea substantially greater length L1 than the sides 10 a, 10 b, of the hole10 closest to the gap 14 and/or the inner sides of the jaws 12, 13 formsmaller angles with the geometric longitudinal axis L of the medullarynail 5, than front portions of said sides 10 a, 10 b. This means thatsubstantially less compressive forces are needed for pressing themedullary nail 5 on the locking screw 9 than for pulling off saidmedullary nail 5 from said screw. If the inner parts 14 a of the gap 14are substantially narrower than the diameter of the hole 10, it mayfurther be almost impossible to remove the medullary nail 5 from thelocking screw 9 unless exceptionally large pulling forces are used.

The locking screw 9 can be replaced by another locking means. Themedullary nail 5 may in a manner known per se consist of a metallicmaterial and may further be designed in a known manner. The snap-indevice 11 of the medullary nail 5 may have jaws 12, 13 with bevelledouter edge portions 12 a, 13 a.

The medullary nail 5 may be designed for use at fractures on other bonesthat an fractures on forearm bones 1. Thus, the medullary nail 5 maye.g. be designed for use at all fractures on tube bones, e.g. radius,fibula, fibia, femur or humerus.

The front parts 5 b of the medullary nail 5 may eventually have a secondtransverse hole 15 behind the hole 10 (shown with broken lines in FIG.2). The locking screw 9 may have a hole 16 (shown with broken lines inFIG. 2) or another attachment member for attaching a fixture (not shown)to the locking screw 9. This fixture can be adapted to guide a drill fordrilling a second hole for a second transverse locking screw (notshown), which shall be screwed through the hole 15.

The medullary nail 5 may eventually be cannulated for threading onto aguide applied in the bone.

1. Device at medullary nails for fixation of bone fragments at bonefractures, wherein a medullary nail (5) is insertable into holes (6) inmedullary canals in the bone fragments (3, 4), and wherein front parts(5 b) of the medullary nail (5) can be locked to one of the bonefragments (3, 4) by means of a locking means (9) which is transverselylocated in the bone fragment and extends through a transverse hole (10)in said front parts (5 b) of the medullary nail (5), characterized thatthe front parts (5 b) of the medullary nail (5) includes a snap-indevice (11) which is designed to be threaded onto the locking means (9)and thereby opened by the locking means (9) and to be snapped-in againto a closed condition (FIG. 4) when the locking means (9) is located inthe transverse hole (10) in the front parts (5 b) of the medullary nail(5) such that the snap-in device (11) retains the medullary nail (5) atthe locking means (9).
 2. Device according to claim 1, characterized inthat the snap-in device (11) is designed to retain the medullary nail(5) in a firm grip at the locking means (9).
 3. Device according toclaim 2, characterized in that the snap-in device (11) is designed toretain the medullary nail (5) at the locking means (9) such that themedullary nail (5) can move neither substantially in axial directionrelative to the longitudinal axis thereof nor rotate in relationthereto.
 4. Device according to claim 1, characterized in that thesnap-in device (11) is designed such that the medullary nail (5) can notloosen or being pulled off from the locking means (9).
 5. Deviceaccording to claim 1, characterized in that the snap-in device (11) hastwo jaws (12, 13) which are provided such that the locking means (9),when the medullary nail (5) is moved in a direction (F) in parallel withits longitudinal axis (L) towards said locking means (9), is locatedbetween said jaws (12, 13), eventually after rotation of the medullarynail (5) about said longitudinal axis (L) if necessary.
 6. Deviceaccording to claim 1, characterized in that the snap-in device (11) hastwo jaws (12, 13) defining a gap (14) of which inner parts (14 a) areopen towards the transverse hole (10) in the front parts (5 b) of themedullary nail (5), that the inner parts (14 a) of the gap (14) have aless width than the diameter of the transverse hole (10) and a lesswidth than the width or diameter of the locking means (9), that the jaws(12, 13) are elastic such that the locking means (9) brings said jaws tospring apart when the snap-in device (11) is threaded onto said lockingmeans, and that the jaws (12, 13) due to their elasticity can springback to their original positions when the snap-in device (11) has beenthreaded so far onto the locking means (9) that said locking means (9)is situated in the transverse hole (10), whereby the snap-in device (11)retains the medullary nail (5) on the locking means (9).
 7. Deviceaccording to claim 6, characterized in that the jaws (12, 13) areprovided such that the gap (14) tapers in a direction towards its parts(14 a) and to the transverse hole (10).
 8. Device according to claim 6,characterized in that the jaws (12, 13) are provided such that outerparts (14 b) of the gap (14) are wider than the locking means (9). 9.Device according to claim 6, characterized in that the jaws (12, 13)have a substantially greater length (L1) than sides (10 a, 10 b) of thehole (10) closest to the gap (14) seen in the longitudinal direction ofthe medullary nail (5), and/or that inner sides of the jaws (12, 13)define or form smaller angles with a geometric longitudinal axis (L) ofthe medullary nail (5) than front portions of sides (10 a, 10 b) of thehole (10) closest to the gap (14).
 10. Device according to claim 6,characterized in that the jaws (12, 13) have bevelled outer edgeportions (12 a, 13 a).
 11. Device according to claim 1, characterized inthat the locking means (9) is a locking screw which is screwed into abone fragment (4) and which can be removed or extracted from thetransverse hole (10) in the front parts (5 b) of the medullary nail (5)by being unscrewed or backed out of the bone fragment (4).
 12. Deviceaccording to claim 1, characterized in that the front parts (5 b) of themedullary nail (5) has a second transverse hole (15) behind said firsttransverse hole (10), and that the transverse locking means (9) has ahole (16) or another attaching member for attachment of a fixturethereto, said fixture being adapted to guide a drill for drilling asecond hole in a lower bone fragment (4) for a second transverse lockingmeans which is adapted to extend through the second transverse hole (15)of the medullary nail (5).
 13. Device according to claim 1,characterized in that said device is adapted to be used at medullarynails (5) for forearm bones, e.g. ulna.